The present invention relates to a substrate potential generating circuit and, more particularly, to a substrate potential generating circuit which supplies stably a predetermined potential to a substrate of a semiconductor integrated circuit.
A conventional substrate potential generating circuit of this kind generally comprises: an oscillation circuit for oscillating a signal of a predetermined frequency; a waveform shaping circuit for wave-shaping the signal from the oscillation circuit into a square-wave signal; and a charge-pump circuit for generating a required substrate potential of a negative polarity which is supplied to the substrate of the semiconductor integrated circuit.
It is an essential and important matter that substrate potential generating circuits as explained above have enough capability of stably supplying a substrate potential to the entire substrate of the semiconductor integrated circuit. For this purpose, it has been necessary in the conventional circuit to increase the size of such components as transistors and a capacitor which constitute the charge-pump circuit and also to have the oscillation frequency of the oscillation circuit made comparatively high, thereby causing a disadvantage in that power consumption inevitably increases. Furthermore, the conventional substrate potential generating circuit has a disadvantage in that there is an increase in the current which is necessary for the generating circuit itself to perform a high-speed switching operation, so that the circuit cannot satisfactorily supply a stable substrate potential to the substrate.